Answers to Questions About Jupiter
Answers to SL9 Data Log
Answers to Questions About Jupiter
- How many kilometers are in one AU? This distance is the mean (or average) distance between what two objects?
One AU equals 149,597,870 km, the mean distance between the Sun and Earth. (This information is in the Nine Planets Glossary, accessible by clicking on the "AU" hotlink on the Jupiter page.)
- Is Jupiter a bright or a faint object in Earth's sky? What objects are brighter than Jupiter? What are some other bright objects that can be seen without a telescope from Earth?
Yes, Jupiter is relatively bright. Only the Sun, the Moon, Venus, and sometimes Mars are brighter. Other bright objects in Earth's sky include Mercury, Saturn, Ganymede, Io, Europa, Uranus, and Callisto. (This information is available on the Jupiter page and in "Solar System Extrema," accessible by clicking on the "brightest" hotlink on the Jupiter page.)
- What is a gas planet? Which of the planets in our solar system are gas planets? Why are they also called "gas giants"?
The gas planets—Jupiter, Saturn, Uranus, and Neptune—are composed primarily of hydrogen and helium. They rotate rapidly and have low densities, rings, and many satellites. These four planets are also classified as giant planets because they have diameters greater than 48,000 km. (This information is in the Overview of the Solar System, accessible by clicking on the "gas planets" hotlink on the Jupiter page.)
- What kind of material makes up Jupiter's core? What is the next layer composed of? What does the word ice mean to planetary scientists?
Jupiter's core is made up of a rocky material. The next layer is composed mainly of liquid metallic hydrogen. It also contains small amounts of helium and various ices, or the solid forms of water, methane, and ammonia that occur in the outer regions of our solar system. (This information is on the Jupiter page and in the Glossary, accessible through the "ices" link.)
- In what states (solid, liquid, or gaseous) does hydrogen exist on Jupiter? What does an observer see when looking at the surface of Jupiter from far away? Would a spacecraft be able to land on the surface of Jupiter? Why, or why not?
The main bulk of Jupiter is composed of liquid metallic hydrogen, and the outermost layer of the planet has ordinary molecular hydrogen in both liquid (nearer the center) and gaseous states. It is the top of this outermost gaseous layer of hydrogen and helium that we see when we observe Jupiter. One reason that a spacecraft could not land on Jupiter is that there is no solid surface on this gas planet. (This information is on the Jupiter page.)
- When was the spacecraft Galileo launched? When did it first encounter Jupiter? What information has the Galileo probe sent back from Jupiter?
Galileo was launched in October 1989 from the Space Shuttle. Its first encounter with Jupiter was scheduled to occur on December 7, 1995. Galileo surveyed Jupiter's moons, and the probe descended 600 km into the planet's atmosphere to provide our first direct evidence of the interior of a gas giant. (This information is on the Jupiter page and the Spacecraft page, accessible through the "Galileo" link.)
- What is the Great Red Spot—what does it look like, how big is it, and what causes it?
The Great Red Spot is a reddish orange oval in Jupiter's atmosphere. It has been observed from Earth since the 1600s. The Spot is about 12,000 by 25,000 km—two Earths could fit inside it. Scientists believe that the Great Red Spot is a high-pressure region whose cloud tops are significantly higher than the surrounding regions. (This information is on the Jupiter page.)
- Why could a gas planet not get much larger than Jupiter?
Jupiter is so large that its strong gravitational force would pull any additional materials in toward the center of the planet, thus preserving its radius. (This information is on the Jupiter page.)
- Does Jupiter have rings? If so, how do they compare to Saturn's rings?
Yes, Jupiter does have rings. They are fainter than Saturn's rings, and most scientists did not believe they were there until they were directly observed by Voyager 1. (This information is on the Jupiter page.)
- When was Comet Shoemaker-Levy 9 discovered, and by whom? When and why did the comet break into 21 fragments? In what way was SL9's collision with Jupiter a "first" for planetary scientists?
SL9 was discovered by Eugene and Carolyn Shoemaker and David Levy in 1993. That same year the comet broke into fragments when it passed by Jupiter within the Roche limit. Within this limit, a planet's tidal (gravitational) forces will cause a smaller body to break apart. SL9 represented the first time scientists were able to observe a collision between two extraterrestrial objects. (This information is on the SL9 page—accessible through the "Comet Shoemaker-Levy 9" link on the Jupiter page—and in the Glossary entry for "Roche limit" that is hotlinked on the SL9 page.)
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Answers to SL9 Data Log
- Before it collided with Jupiter, for how many years do scientists believe SL9 had orbited the planet? About how many years did it take for the comet to orbit Jupiter once?
Scientists estimate that SL9 had been orbiting Jupiter for at least two decades, with an orbital period of about two years. (This information is on the comet page at the NSSDC site.)
- What system did scientists use to name each fragment of SL9? Which fragment was thought to be the largest, and why?
The fragments were assigned letters from A to W (excluding I and O). Fragment Q was believed to be the largest because it appeared brightest. (This information is on the comet page at the NSSDC site.)
- The impacts occurred on the far side of Jupiter, from Earth's perspective. How were we able to observe the effects of the collision? How long did scientists on Earth have to wait to get a look at the impact sites?
Scientists had to wait for Jupiter to rotate so that the impact sites were facing Earth. This took about 11 minutes. Since Jupiter is so far from Earth, the scientists then had to wait about 48 minutes for light to travel from Jupiter to Earth. (This information is on the impact page at the NSSDC site.)
- What was the predicted date and time of impact of fragment Q1? When did it actually hit?
Fragment Q1 was expected to strike Jupiter on July 20, 1994, at about 8:04 p.m. It actually hit at about 8:12 p.m. that day. (This information is on the impact page at the NSSDC site.)
- Describe what happened when a fragment hit Jupiter.
Each fragment traveled through the atmosphere and then exploded, creating a fireball that rose back above the cloud tops. The explosion produced pressure waves in the atmosphere and "surface waves" at the cloud tops. The rising material may have been a mixture of vaporized comet and Jovian atmosphere. (This information is from the impact page at the NSSDC site. The article "A Comet's Fiery Dance at Jupiter," from the May 1995 Galileo Messenger, gives a similar account.)
- The Hubble Space Telescope was used to observe activities on Jupiter during the comet's impact. What unusual events involving Jupiter's aurorae (glowing gases in the atmosphere) did HST reveal? What comet fragment caused this activity?
Fragment K disrupted the radiation belts around Jupiter, resulting in a temporary, bright glow in the aurorae. Astronomers believe the K impact created an electromagnetic disturbance that scattered charged particles into Jupiter's upper atmosphere. Unexpectedly bright X-ray emissions were also detected near the time of the K impact. (This information is in the article "Hubble Observations Shed New Light on Jupiter Collision," on JPL's list of Latest Conclusions.)
- What have scientists learned from data collected after the comet's impact? Specifically, what have they learned about Jupiter's wind patterns?
Scientists have tracked the clouds of dust and smoke released into Jupiter's atmosphere to learn about the wind patterns there. They've discovered that winds in the upper atmosphere travel in different directions than those in the lower levels. In some regions, the SL9 dust in the upper atmosphere traveled north, away from the southern polar, whereas other regions showed no evidence of this northerly wind. Dust in lower atmospheric levels has been carried east/west. (This information is available at the STSI site [see Reference Shelf], on the page dealing with Jupiter winds.)
Return to the Comet Shoemaker-Levy 9 Page.